Specialty electric vehicles (EVs) of various types are well known for indoor applications (for example, forklifts, wheelchairs, and airport people-movers for the elderly) and for short-trip outdoor use (golf carts, neighborhood electric vehicles, and handicapped scooters). Such vehicles typically are purely electric, having a motive electric motor powered by a battery storage system that is recharged by being connected to a regional electric grid or other electric source during periods of non-use of the vehicle.
Purely electric vehicles for use on open roads and highways have been shown to have credible niche markets in the USA and Europe only when the cost to the consumer is subsidized in some fashion. A key issue for future mass viability is whether technical maturity and higher volume production can meet the market-demanded price level.
EVs are well suited to short trip, low speed duty cycles in temperate climates. They are not well suited to higher mileage, higher speed, and longer trip patterns of driving in the USA, nor to operation in cold weather; however, land use, climate, and population density in many parts of the world are well-suited to EV use. For example, average vehicle speed and trip length are dramatically lower in Tokyo or Beijing, or even in London, Paris, or Mexico City, than in Detroit or Los Angeles. Vehicle attributes like top speed and peak horsepower are not likely to be so important in those foreign markets.
Electric road vehicles are highly desirable for meeting ZEV and PZEV standards, as witnessed by the success of recent trials in California. However, battery technology has been and continues to be the limiting factor in terms of cost, functionality (range), and durability of EV systems. Battery systems required to provide purely electric vehicles with a reasonable range and speed are still excessively bulky and costly. Therefore, the automotive industry has largely moved on to research and development of other approaches to provide continuous electric power to vehicles and to thereby gain the benefits of extremely low emissions and reduced fossil fuel consumption.
Because prior art road EVs, even those having very large capacity batteries, have limited range, it is of interest to provide onboard electric recharging capability. Such EVs are known in the prior art as “range extender” EVs or “hybrid” EVs. In a so-called “first generation” hybrid EV, typified by the Toyota Prius, all of the electric power used to charge the battery is generated onboard through a combination of regenerative braking and an internal combustion engine (ICE) driving an electric generator. The battery required is much smaller than in a purely electric EV. Fuel efficiency gains come from downsizing the ICE, operating the ICE at a more efficient operating point (when running), and shutting off the ICE during periods of low power demand.
One approach for a “second generation” EV, which is an evolution of the current series/parallel hybrid electric vehicle, is to increase the capacity of the battery and to allow the battery to operate in a charge-depleting mode without simultaneous recharge for a period of time, permitting short trips at low speed in pure electric mode. The battery may be recharged afterward when the vehicle is parked by being plugged into a source of power such as a regional electric grid. This then becomes a “plug-in” hybrid electric vehicle, where low speed and short trips can be substantially grid fueled and an onboard internal combustion engine (ICE) provides increased peak power and extended range for higher speed and longer trip operation. Thus the electric energy stored in the battery initially is complemented by the chemical energy stored in the ICE hydrocarbon fuel tank, typically a gasoline tank, providing a greatly extended driving range and full utility to the driver.
A disadvantage of any ICE hybrid system, however, is the level of combustion emissions characteristic of an ICE, requiring expensive and complex emission controls. Despite advances in emissions control technology, an ICE still produces gaseous emissions, including some level of carbon monoxide, and cannot be operated safely for extended periods in a structure with limited ventilation such as a closed garage. Another non-toxic but undesirable ICE emission is carbon dioxide which contributes to global warming.
Another disadvantage of an ICE hybrid system is its relatively low efficiency in terms of fuel-to-electric conversion and fuel-to-thermal conversion. This lowers the efficiency of the vehicle when the ICE is running, especially in cold weather conditions.
Another approach in a range extender EV is to use a fuel cell assembly (FC) in place of an ICE and generator. In the prior art, such a vehicle is known as a fuel cell EV (FCEV). As in the ICE/generator configuration, the FC reduces the weight and size of battery required. Significant advantages of a fuel cell assembly over an ICE/generator are that a fuel cell is essentially silent, high in efficiency, and inherently low in toxic emissions.
An example of an FCEV is the Toyota FINE-N H2 FCEV, shown at the 2003 Toyota Motor Show, which uses hydrogen directly rather than reformed hydrocarbon as the chemical fuel for the FC, thus obviating the need for a reformer and post-FC combustion. All FCEVs are series hybrids and all require some amount of battery storage for system start-up and transient response reasons.
Some developers of FCEVs use proton exchange membrane (PEM) fuel cells and are focused on fuel cell dominant systems. This requires a fuel cell of 50-100 kW peak power for a typical car or light truck and places severe demands on fuel cell start-up and transient response. Such a large fuel cell is clearly a substantial cost challenge using present-day technology. Also, expectations of 15 year battery life for Ni metal hydride (NiMH) batteries in Toyota's existing hybrid vehicles suggest that a more battery-dominant FCEV is practical. The Toyota FINE-N H2 FCEV concept vehicle appears to be battery-dominant which, due to regenerative braking and operating the fuel cell in a high efficiency window, explains the very high range of 500 km on a tank full of compressed H2.
Extending the range of a PEM FCEV requires onboard generation and storage of hydrogen. A serious problem in the art is that PEM fuel cells are intolerant of CO in the hydrogen fuel stream, such as is generated by a typical hydrocarbon catalytic reformer. Thus, generating hydrogen onboard by reforming hydrocarbons requires a large, complex, multistage reformer and gas cleanup system to make the H2 of sufficient purity to run the PEM fuel cell. Further, the cost, size, transient response, and start-up time realities of such a PEM reformer make a buffer of stored H2 essential, adding further cost and complexity. For these reasons, a PEM hybrid vehicle is ill-suited for range-extended operation by reforming hydrocarbons onboard.
A solid oxide fuel cell (SOFC) is another known class of fuel cell capable of utilizing a mixed fuel containing both hydrogen and carbon monoxide generated by a simple hydrocarbon reforming process. At the high temperature conditions pertaining within an SOFC, not only H2 but also CO and residual light hydrocarbons may be consumed in the fuel cell anode. Further, the exhaust of an SOFC is hot and still rich in hydrogen (known in the art as “syngas”) whereas the exhaust of a PEMFC is relatively cold and of little additional use. Syngas can be used for a variety of purposes, for example, for enhanced combustion and aftertreatment in an ICE; for recirculation into the reformer to permit highly efficient endothermic reforming; or for combustion directly to yield additional high-quality (high-temperature) heat for other uses. The heat can be used for premium vehicle heating and accelerated engine and catalyst warm-up and/or to drive a bottoming cycle such as a gas turbine (GT) or expander to recover additional power.
As an auxiliary power unit (APU) in a vehicle, an SOFC APU can extend the operating range up to 400-650 km or greater, depending upon the size of the fuel tank. Because “waste” heat is readily available, an SOFC EV may operate in cold climates without the compromise to range and efficiency typical of PEM EVs. Further, an SOFC is especially attractive as a range extender because of the efficiency of heat recovery for HVAC functions.
An especial advantage of SOFC system in a vehicle is that it represents an independent source of electricity, syngas, and high-quality heat, all of which may be used for non-vehicular purposes during periods when the vehicle is parked and out of service. What is needed in the art is a method and apparatus for utilizing those properties to advantage during vehicle shutdown periods after the vehicle battery is fully recharged by the SOFC and/or is plugged into a regional electric grid for recharging. Such usage can substantially increase the cash flow rate of return of the automotive investment in an SOFC system.
It is a principal object of the present invention to utilize a vehicle-based APU system, and preferably an SOFC APU system, for non-vehicular uses during periods of shutdown of the vehicle.